The secondary batteries are used in various uses and, among them, a lithium ion secondary battery, in which charge and discharge take place as lithium ions move between positive and negative electrodes, is preferably used as a battery for moving vehicles such as an automobile, an electric motorcycle, an electric bicycle because it has the following battery characteristics: high mass energy density and high volume energy density.
The lithium ion battery used for a drive power source or an auxiliary drive power for an automobile, an electric motorcycle, an electric bicycle, and the like mainly includes a type obtained by accommodating a columnar body around which positive and negative electrodes are stacked and wound via separators in a metal casing and a type obtained by accommodating a flat body in which positive and negative electrodes are stacked via separators in a package.
Among the above lithium ion secondary batteries, the flat lithium ion secondary battery is preferably used as a battery for a power source for motor drive or the like because it is capable of easily increasing a unit cell capacity by increasing areas of the positive and negative electrodes or by increasing the number of positive and negative electrodes to be stacked.
As for a unit battery of the flat lithium ion secondary battery, it is possible to make effective use of high energy density that the lithium ion secondary battery has by packaging battery elements with a film material.
It has been proposed a configuration in which a plurality of film-casing batteries (unit batteries) which are conductively connected to each other and stacked via heat insulating and cushioning sheet members are secured by a tape as a binding member in order to prevent displacement between the unit batteries due to vibration in transportation (refer to, e.g., Patent Document 1).